Patent GB-780749-A (GB)
Title: Data storage system including searching, reading and recording apparatus
IPC: G11B27/10
Filed: 1955-09-21
Abstract: 780,749. Electric digital-data-storage apparatus. NATIONAL CASH REGISTER CO. Sept. 21, 1955 [Oct. 18, 1954], No. 26947/55. Class 106 (1). In an electrical data storage system, apparatus for locating on a magnetic tape a particular block defined by an address and for subsequently reading information from or recording information into the block, the tape being fed in either direction past a magnetic read-record head for sensing addresses recorded in the blocks thereof, includes a register for storing a required address, and a comparator adapted to receive simultaneous signals indicative of the stored address and the address sensed from the tape and including a decision device for controlling tape feed, whereby the direction of tape feed is changed from forward to reverse when the sensed tape address is greater than or equal to the stored address, and the tape feed in the reverse direction is interrupted when the two addresses are equal. As described, the magnetic tape 140, Fig. 1, forms an auxiliary store for a computer 100. The tape is driven by a two-speed motor 144 which continually rotates capstans 142, 143 in opposite directions. A solenoid 155 or 151 is energized from drive control unit 131 to engage roller 139 or 152 with capstan 143 or 142 for forward or reverse movement respectively. The tape has 5 pairs of duplicate channels comprising clock pulse channels Ca, Cb, and information channels Ch1a-4a, Ch1b-4b, Fig. 2, in which decimal digits are recorded, in synchronism with the clock pulses, in excess-three binary coded form. The information, recorded by the non-return-tozero method, is divided into blocks each comprising 12 words WS and WO-W10. Words WO-W10 each comprise 11 decimal digit positions PO-P10 plus a reference-zero position Pb, and WS comprises Pb plus a blank area Bx in which no information or clock pulses are recorded. The 10,000 blocks on a tape are defined by consecutive 4-digit address numbers in positions P2-P5 of WO. The digit and word periods are marked by outputs from counters 108, 109 controlled by clock pulses sensed from the tape and amplified and shaped in clock reader 142a. The clock pulses may be obtained originally from rotating soft iron gearwheel 720 having evenly spaced teeth and a blank portion around its periphery. Each tooth produces a pulse in head 721 which, if switch 723 is thrown over, is applied via 142a and line 101 to recorder 122 whose otputs are fed to the clock heads 125, 127, Fig. 2, of the multiple read-record head 130. The drive control unit 131 is controlled by auxiliary clock pulses Co from multivibrator 154. The recorder receives decimal digits to be recorded in the information channels on the tape from the computer 100 via line 107, link 115 and line 121. Information read from the tape is passed via reader 112 and line 117 to the link 115, line 107 and the computer. The line 107 represents four parallel information lines and a fifth line which supplies a stop signal from the computer via 115, line 183 and the comparator 114 to the drive control imit 131 when, it is desired to stop a reading or recording operation. The computer can send one of three commands: " search," read " or " record," over line 106 (representing three parallel lines) to the tape circuitry shown. For a search command, the required address, comprising four excess-three binary-coded decimal digits, is applied from line 105 (representing sixteen parallel lines) to sixteen electromagnetic relays in register 116, and, after a time delay to ensure that the address has been stored, a signal is applied over line 181 to unit 131 to cause the tape to be driven forward at high speed ; at the same time a releasing signal is applied to the computer. The address from 116 is applied over 164 to comparator 114 in synchronism with the block addresses read out from the tape through reader 112. When the tape address is greater than or equal to the required address in 116, a signal on line 133 reverses the tape drive ; the decimal digits of the address from 116 are then applied to the comparator in reverse sequence and when subsequently the compared addresses are equal, a further signal on 133 stops the tape at the blank portion Bx of the required block. For a read or record command, the tape is moved forward at the slower speed, and a pulse over 105 energizes one of three relays in 116 according to whether recording or reading of addresses, numerical information or both is required ; the recorder-control output Q 1 on line 120 and gated clock pulses Cs or 104 are rendered operative for corresponding periods (WO and/or W1-10). The tape circuitry consists primarily of bi-stable Eccles-Jordan type trigger circuits (called " flip-flops ") and logical diode gating networks. The reading circuits 142a, 112 include means for compensating for the two different tape speeds. The clock reader 142a includes also gates to inhibit short duration spurious signals induced from adjacent heads in 130 and to cause a fall in potential of the square clock pulse output at the same time for both forward and reverse tape movement.